Field of the Invention
The present disclosure relates to an antenna apparatus and a beam-forming method thereof, and more particularly, to a beam-forming technology in a single radio frequency (RF) based antenna.
Description of the Related Art
Due to the diffusion of smart devices and the increase of the multimedia services, the mobile service traffic bursts and, accordingly, an increase in the capacity of a communication system is required. Various methods for improving the performance of a wireless communication system including a beam-forming method are studied. Unlike an omni-antenna which radiates radio wave in all directions, the beam-forming method sets a different antenna gain depending on a direction to improve the performance of a wireless section.
If a beam-forming antenna is used, in a transmitter side, the radio wave with an enhanced antenna gain may be focused to radiate in a specific direction or a null may be formed not to radiate the radio wave in a specific direction so that the reception signal quality of a receiver becomes higher. In addition, in the receiver side, the radio wave may be selectively received depending on a reception direction to amplify a desired signal and reduce the interference so that the quality of wireless link may be enhanced.
The beam-forming method may obtain an effect such as a capacity increase due to spatial reuse, an interference cancellation between adjacent nodes that use the same frequency, the distance increase even though the same transmission power, and the like. In order to implement such a beam-forming function, a beam-forming antenna that can control the antenna gain according to a direction is required. In this case, a smart antenna which is configured of a plurality of antennas of an array form is usually used.
However, since such an array antenna should use multiple Radio Frequency (RF) chains, it has a disadvantage in that the volume is large and power consumption is also large, it is difficult to apply to a mobile terminal, and usually used to a base station. As a beam-forming antenna for applying to the mobile terminal, a single RF-based switched parasitic antenna (SPA) or an electronically steerable passive array radiator (ESPAR) antenna has been proposed.
The SPA or the ESPAR is configured of one active antenna and a plurality of passive antenna, and the active antenna is connected with an RF end and the plurality of passive antenna are connected with an on/off switch or a variable resistor element. By adjusting the switch of the passive antenna or the resistance value of a variable resistor, a directional beam is formed using a mutual coupling of the active antenna and the passive antenna to obtain a beam-forming effect. Since this single RF-based beam-forming antenna is configured as one RF, it is expected to be easily applicable to the mobile terminal as the power consumption is small and the size and the volume are small.
Meanwhile, in a multi-path wireless channel environment, various diversity methods are used to overcome the fading phenomena of a wireless channel. This diversity method is a method of receiving the same signal which performs an independent fading using N-array antennas and combining the signals through a signal processing method. In particular, a reception diversity method which is applied in a receiving end includes a selection combining (SC), a maximum ratio combining (MRC), an equal gain combining (EGC), and the like. The SC is a method of selecting and receiving one antenna which has the best signal quality (SINR) from among the N reception antennas. The MRC is a method of setting a reactance value for each reception antenna and adjusting a gain and a phase so that the reactance value may have a matched filter form with respect to a channel matrix to obtain an optimum SINR.
The EGC is a method of adjusting only the phase while fixing the gain to a constant in the MRC method. The SC has the lowest complexity, but also has the lowest performance. The MRC method has the best performance, but it is known that the EGC method has a performance close to the MRC in consideration of a complexity.
In the related art, in order to apply such a reception diversity, N array antennas are used to receive a signal and a RF chain is mounted for each antenna so that a receiver may be configured in an architecture which can process signals independently. Therefore, in the above described single RF based antenna structure, as the RF chain is a single, multi-path reception signals cannot be combined. Therefore, even if signals are received in multi-paths, a single path should be selected form the multi-paths to form a single beam in a corresponding direction and receive a signal.
Hence, conventionally, in the single RF based antenna structure, the beam-forming using a single beam is mainly applied, and the beam-forming using multi-beam is not used.